When a distributed generator is connected with a distribution system, a voltage at a point of common coupling with the distributed generator is increased by active power of the distributed generator injected into the distribution system.
The voltage at the point of common coupling with the distributed generator is increased because an active output is injected into a point of common coupling with the distribution system in such a way that a flow of power from the point of common coupling to a substation, that is, a normal direction flow of power in the distribution system and a reverse direction flow of power occur, thereby increasing the voltage to a degree of the product of a current and a line impedance at that time.
Accordingly, power suppliers restrict a capacity of the distributed generator in connection with a distribution system to prevent a voltage at a point of common coupling with the distributed generator from exceeding a tolerance range due to the distributed generator.
Particularly, it is difficult to additionally connect a distributed generator with a distribution line in connection with existing distributed generators due to a voltage rise at a point of common coupling with the distributed generator. This is because applications for connecting a distributed generator converge on regions having similar location requirements. Also, as a result, even though a capacity of a distributed generator to be newly connected is small, it may be impossible to connect.
To connect a distributed generator not allowed to be connected, it is necessary to detect a new point of common coupling with the distributed generator at another distribution line or to build a new exclusive distribution line from a substation. However, in this case, it is impossible to start business due to excessive costs.
Such technical limitation of conventional technologies socially causes a loss in opportunity cost and becomes an obstacle in a new renewable energy supply policy and an eco-friendly policy for restraining carbon dioxide discharge.
The related art of the present invention is disclosed in Korea Patent Publication No. 10-2012-0025121 (Mar. 15, 2012) under the title of “An optimal voltage control system and method for dispersed generation interconnected primary distribution line.”